CO2 Seeping Into Water Supply
Discovery.com, Nov. 18, 2008
Groundwater seems to be taking on carbon dioxide 100 times faster than the atmosphere, according to a new study.
As humans pump billions of tons of CO2 into the atmosphere each year, the planet is rapidly growing saturated. Water readily dissolves the gas to form an acid, and over the last century Earths oceans have already been lowered from a pH of 8.1 to 8.0.
Gwen MacPherson of the University of Kansas and a team of researchers have now made an analogous discovery in the groundwater flowing beneath the pristine Konza Prairie in Kansas. From 1991 through 2005, dissolved CO2 levels went up about 20 percent.
"In the atmosphere, CO2 went up 23 parts per million during that time," MacPherson said. "It went up 2,100 ppm in the water, so that's actually quite a lot."
Ocean acidification is a major threat to corals, clams and any shell-forming animals; as pH declines, the water becomes corrosive and eats away at the creatures' hard exteriors.
Recent experiments designed to test the risks of burying anthropogenic carbon underground have shown that CO2 can turn groundwater into an acid, too. If a reservoir of CO2 were to leak into an aquifer, water that humans rely on for irrigation and drinking water could start leeching heavy metals, benzene, and poisonous gases out of the surrounding rock.
"Most people are worried about CO2 escaping from below and coming up," Yousif Kharaka of the United States Geological Survey in Menlo Park, Calif., said. "If it does, it's going to bring all kinds of things with it."
As part of the Department of Energy-funded Zero Emissions Research Technology (ZERT) project, Kharaka and colleagues injected 660 pounds of CO2 per day into shallow groundwater in Montana. Iron, manganese, calcium and magnesium concentrations all skyrocketed, as did several other contaminants.
Kharaka's study sent dissolved CO2 content soaring to between 50 and 60 times its natural level, far higher than anything MacPherson's team has seen. And she admits that because of the complex role plants play in drawing CO2 out of the atmosphere and injecting it into the soils, she's still unsure whether the atmosphere is the direct cause of the increase.
"But if I'm right, and the increase is linked to the atmosphere, we should see this signal in other places, too," she said.
"I think this is an interesting twist," Kharaka said of MacPherson's study. "There is no doubt that with higher CO2 in the atmosphere, it's going to get into the water. The question is how much of the minerals will dissolve, and how much of an impact it will have at the low levels talked about here."